1. Field of the Invention
The present invention relates generally to image pickup units and, more particularly, to an image pickup unit using charge coupled devices (CCD) which has a comparatively small number of component integrated circuits (IC) and in which the number of wiring lines for connection between ICs can be reduced.
2. Description of the Related Art
Generally, CCD image pickup units presently used in video cameras for home and personal use are IT (interline transfer) type CCD image pickup units, which are ordinarily constituted of a timing generator, a vertical transfer register driver, an electronic shutter driver and a CCD solid-state image pickup. Transfer in vertical transfer registers is performed with transfer pulses in four phases, and reading from each of pixels is performed with two read pulses. Transfer in a horizontal transfer register is performed with transfer pulses in two phases. A reset pulse is required for driving a reset transistor for resetting a floating diffusion region, which corresponds to an output point at the time of reading.
If irising is automatically performed by an electronic shutter function, it is necessary to supply electronic shutter pulses to a substrate bias circuit.
FIG. 14 is a schematic diagram of the configuration of a conventional CCD image pickup unit for cameras.
In the figure are illustrated a timing generator a, a CCD solid-state image pickup b, a vertical transfer register driver c and an electronic shutter driver d. Each of numerals 3, 4, 6, 1, 1 written at lines in the figure represents the number of kinds of pulses. Pulses H1 and 2 are transmitted directly from the timing generator a to (a horizontal transfer register of) the CCD solid-state image pickup b as transfer pulses for horizontal transfer registers. A reset pulse RG for driving a reset transistor is also transmitted directly to the CCD solid-state image pickup b.
Pulses V1 to V4 for transfer pulses for the vertical transfer registers and pulses SG1 and SG2 are output from the timing generator a to the vertical transfer register driver c. The vertical transfer register driver c forms vertical transfer pulses .phi.V1 to .phi.V4 on the basis of the pulses V1 to V4 and SG1 and SG2 and sends the vertical transfer pulses .phi.V1 to .phi.V4 to (the vertical transfer registers of) the CCD solid-state image pickup b.
Further, a shutter pulse DSUB is sent from the timing generator a to the electronic shutter driver d. The driver d forms a shutter pulse .phi.DSUB on the basis of the shutter pulse DSUB and sends the shutter pulse .phi.DSUB directly to (a substrate bias circuit of) the CCD solid-state image pickup b.
FIG. 15 is a diagram of the configuration of the conventional CCD solid-state image pickup b. The CCD solid-state image pickup b has an image pickup area b, light receiving diodes f which correspond to the pixels. The vertical transfer registers are indicated by g, the horizontal transfer register is indicated by h. The horizontal transfer register h is controlled by the above-mentioned reset pulse RG. The substrate bias circuit, indicated by j, is formed of voltage-dividing resistors R1 and R2 and a diode D1. A voltage divided by the voltage-dividing resistors R1 and R2 is normally applied to the substrate through the diode D1. When shutter pulse .phi.DSUB (e.g., 20 V) is applied, the potential of the substrate becomes equal to such a high level that charge accumulated in each pixel element f is forced to discharge to the substrate. This pulse .phi.DSUB has substantially no influence upon other components because of the reverse current checking function of the diode D1.
The conventional CCD image pickup unit has a drawback in that the number of wiring lines between the CCD solid-state image pickup and the other ICs and between the ICs other than the CCD solid-state image pickup is large and there is, therefore, a limit to the reduction in the size of a video camera using the CCD image pickup unit.
More specifically, the number of the kinds of pulses output from the timing generator a to control the CCD solid-state image pickup b is ten. That is, there are reset pulse RG, horizontal transfer pulses H1 and H2 (transmitted directly to the CCD solid-state image pickup b), vertical transfer pulses V1 to V4, readout pulses SG1 and SG2 (sent to the vertical transfer register driver c), and electronic shutter pulse DSUB (sent to the electronic shutter driver d).
The number of the kinds of pulses input to the CCD solid-state image pickup b is eight, smaller by two than ten, the number of the kinds of pulses output from the timing generator a to control the CCD solid-state image pickup. This is because readout pulses SG1 and SG2 are superimposed on vertical transfer pulses V1 and V3, respectively, to be input to the CCD solid-state image pickup b by being included in .phi.V1 and .phi.V3. Consequently, a total of fifteen pulse lines are provided for wiring between the timing generator, the drivers and the CCD.
A CCD image pickup unit having such a large number of wiring lines between the chips constituting the unit has a large overall size and requires complicated wiring operations, which results are contrary to the present demand for smaller and low-priced CCD image pickup units' for home use and are, therefore, undesirable. The demand for a reduction in the size of CCD image pickup units for use in endoscopes is much stronger than that in the case of CCD image pickup units for home use. Thus, there is a strong demand for CCD image pickup units improved in this respect.